PRIME MOVERS AND POWER PLANT MACHINERY.
boiler and travels into the furnace as the endless chain is moved by
the sprockets. The clinkers and ash fall into the ash pit, through
which the grate returns.
Combustion of coal and furnace design have been discussed in
other publications of the Bureau of Mines6 and will not be given
further consideration here.
OIL AS FUEL.
Oil as boiler fuel is most used in gas-depleted oil fields producing
heavy crude oil, or in gas-depleted oil fields near refineries that pro-
duce fuel oil as a by-product.
The evaporative effect per pound of most crude oils and fuel
oils is about the same. Fuel oils generally range in gravity from
14 B. to 290 B., and their flash points are not less than 1500 F.
A fuel oil should be free from water and solid matter in suspension.
The proper combustion of fuel oil depends on the characteristics of
the oil, the type of burner used, the design of the furnace or fire
box, and proper care.
COMBUSTION OF FUEL OIL.
Fuel oil is not burned as a vapor but as a heavy mist. Generally
the type of burner that gives the greatest degree of atomization is
the most efficient. In some burners the oil is atomized by forcing
it through a small aperture under pressure; in others it is atomized
by a stream of air or steam. Steam atomizers usually take about 3
per cent of the steam generated, and high-pressure steam usually is
more satisfactory than low-pressure. With oil the amount of pres-
sure differs with different types of burners from a few pounds to
60 or 70 pounds to the square inch. Low-pressure systems are gen-
erally used under standpipe pressure.
For proper combustion the air supply must be carefully regu-
lated. Smoke, often caused by insufficient air or improper mixing,
is prevented by admitting additional air through the bridge wall.
Dutch ovens are sometimes built in front of boiler furnaces, when
fuel oil is used, to increase the volume of the combustion chamber
and to preheat the air used for the combustion mixture. A company
in the Casmalia field, California, claims a fuel saving of more than
20 per cent after the installation of Dutch ovens at the stills of their
topping plant there.
6 Flagg, S. B., Cook, G. C., and Woodman, F. E., Experiments with furnaces for a
hand-fired return tubular boiler: Tech. Paper 34, Bureau of Mines, 1916, 32 pp. Clem-
ent, J. K., Frazer, J. C. W., and Augustine, C. E., Factors governing the combustion of
coal in boiler furnaces, a preliminary report: Tech. Paper 63, Bureau of Mines, 1914, 46
pp. Kreisinger, Henry, Hand firing soft coal under power-plant boilers: Tech. Paper 80,
Bureau of Mines, 1915, 83 pp. Saving coal in boiler plants: Tech. Paper 205, Bureau of
Mines, 1918, 24 pp.
George, H. C. Surface Machinery and Methods for Oil-Well Pumping. Washington D.C.. UNT Digital Library. http://digital.library.unt.edu/ark:/67531/metadc12407/. Accessed October 22, 2014.